Parse the mem_encrypt= command line parameter from the EFI stub if
CONFIG_ARCH_HAS_MEM_ENCRYPT=y, so that it can be passed to the early
boot code by the arch code in the stub.

This avoids the need for the core kernel to do any string parsing very
early in the boot.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240227151907.387873-16-ardb+git@google.com

The secondary startup code is used on the primary boot path as well, but
in this case, the initial part runs from a 1:1 mapping, until an
explicit cross-jump is made to the kernel virtual mapping of the same
code.

On the secondary boot path, this jump is pointless as the code already
executes from the mapping targeted by the jump. So combine this
cross-jump with the jump from startup_64() into the common boot path.
This simplifies the execution flow, and clearly separates code that runs
from a 1:1 mapping from code that runs from the kernel virtual mapping.

Note that this requires a page table switch, so hoist the CR3 assignment
into startup_64() as well. And since absolute symbol references will no
longer be permitted in .head.text once we enable the associated build
time checks, a RIP-relative memory operand is used in the JMP
instruction, referring to an absolute constant in the .init.rodata
section.

Given that the secondary startup code does not require a special
placement inside the executable, move it to the .text section.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240227151907.387873-15-ardb+git@google.com

Determining the address of the initial page table to program into CR3
involves:
- taking the physical address
- adding the SME encryption mask

On the primary entry path, the code is mapped using a 1:1 virtual to
physical translation, so the physical address can be taken directly
using a RIP-relative LEA instruction.

On the secondary entry path, the address can be obtained by taking the
offset from the virtual kernel base (__START_kernel_map) and adding the
physical kernel base.

This is implemented in a slightly confusing way, so clean this up.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240227151907.387873-14-ardb+git@google.com

Assigning the 5-level paging related global variables from the earliest
C code using explicit references that use the 1:1 translation of memory
is unnecessary, as the startup code itself does not rely on them to
create the initial page tables, and this is all it should be doing. So
defer these assignments to the primary C entry code that executes via
the ordinary kernel virtual mapping.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240227151907.387873-13-ardb+git@google.com

When paging is enabled, the CR4.PAE and CR4.LA57 control bits cannot be
changed, and so they can simply be preserved rather than reason about
whether or not they need to be set. CR4.MCE should be preserved unless
the kernel was built without CONFIG_X86_MCE, in which case it must be
cleared.

CR4.PSE should be set explicitly, regardless of whether or not it was
set before.

CR4.PGE is set explicitly, and then cleared and set again after
programming CR3 in order to flush TLB entries based on global
translations. This makes the first assignment redundant, and can
therefore be omitted. So clear PGE by omitting it from the preserve
mask, and set it again explicitly after switching to the new page
tables.

  [ bp: Document the exact operation of CR4.PGE ]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240227151907.387873-12-ardb+git@google.com

x86_64 zero extends 32-bit operations, so for 64-bit operands,
XORL r32,r32 is functionally equal to XORQ r64,r64, but avoids
a REX prefix byte when legacy registers are used.

Slightly smaller code generated, no change in functionality.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240124103859.611372-1-ubizjak@gmail.com

Now that the proper section and file alignment is used, and the EFI
memory attributes protocol to manage executable permissions where needed
is invoked, set the NX compat flag unconditionally.

  [ bp: Remove the "we"s. ]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240116085347.2193966-2-ardb+git@google.com

Instead of loading a duplicate GDT just for early boot, load the kernel
GDT from its physical address.
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20240226220544.70769-1-brgerst@gmail.com

early_top_pgt[] is assigned from code that executes from a 1:1 mapping
so it cannot use a plain access from C. Replace the use of
fixup_pointer() with RIP_REL_REF(), which is better and simpler.

For legibility and to align with the code that populates the lower page
table levels, statically initialize the root level page table with an
entry pointing to level3_kernel_pgt[], and overwrite it when needed to
enable 5-level paging.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240221113506.2565718-24-ardb+git@google.com

The early statically allocated page tables are populated from code that
executes from a 1:1 mapping so it cannot use plain accesses from C.
Replace the use of fixup_pointer() with RIP_REL_REF(), which is better
and simpler.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240221113506.2565718-23-ardb+git@google.com

'__supported_pte_mask' is accessed from code that executes from a 1:1
mapping so it cannot use a plain access from C. Replace the use of
fixup_pointer() with RIP_REL_REF(), which is better and simpler.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240221113506.2565718-22-ardb+git@google.com

early_dynamic_pgts[] and next_early_pgt are accessed from code that
executes from a 1:1 mapping so it cannot use a plain access from C.
Replace the use of fixup_pointer() with RIP_REL_REF(), which is better
and simpler.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240221113506.2565718-21-ardb+git@google.com

'phys_base' is assigned from code that executes from a 1:1 mapping so it
cannot use a plain access from C. Replace the use of fixup_pointer()
with RIP_REL_REF(), which is better and simpler.

While at it, move the assignment to before the addition of the SME mask
so there is no need to subtract it again, and drop the unnecessary
addition ('phys_base' is statically initialized to 0x0)
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240221113506.2565718-20-ardb+git@google.com

There are two code paths in the startup code to program an IDT: one that
runs from the 1:1 mapping and one that runs from the virtual kernel
mapping. Currently, these are strictly separate because fixup_pointer()
is used on the 1:1 path, which will produce the wrong value when used
while executing from the virtual kernel mapping.

Switch to RIP_REL_REF() so that the two code paths can be merged. Also,
move the GDT and IDT descriptors to the stack so that they can be
referenced directly, rather than via RIP_REL_REF().

Rename startup_64_setup_env() to startup_64_setup_gdt_idt() while at it,
to make the call from assembler self-documenting.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240221113506.2565718-19-ardb+git@google.com

We are going to queue up a number of patches that depend
on fresh changes in x86/sev - merge in that branch to
reduce the number of conflicts going forward.

Also resolve a current conflict with x86/sev.

Conflicts:
	arch/x86/include/asm/coco.h
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Pull bcachefs fixes from Kent Overstreet:
 "Some more mostly boring fixes, but some not

  User reported ones:

   - the BTREE_ITER_FILTER_SNAPSHOTS one fixes a really nasty
     performance bug; user reported an untar initially taking two
     seconds and then ~2 minutes

   - kill a __GFP_NOFAIL in the buffered read path; this was a leftover
     from the trickier fix to kill __GFP_NOFAIL in readahead, where we
     can't return errors (and have to silently truncate the read
     ourselves).

     bcachefs can't use GFP_NOFAIL for folio state unlike iomap based
     filesystems because our folio state is just barely too big, 2MB
     hugepages cause us to exceed the 2 page threshhold for GFP_NOFAIL.

     additionally, the flags argument was just buggy, we weren't
     supplying GFP_KERNEL previously (!)"

* tag 'bcachefs-2024-02-25' of https://evilpiepirate.org/git/bcachefs:
  bcachefs: fix bch2_save_backtrace()
  bcachefs: Fix check_snapshot() memcpy
  bcachefs: Fix bch2_journal_flush_device_pins()
  bcachefs: fix iov_iter count underflow on sub-block dio read
  bcachefs: Fix BTREE_ITER_FILTER_SNAPSHOTS on inodes btree
  bcachefs: Kill __GFP_NOFAIL in buffered read path
  bcachefs: fix backpointer_to_text() when dev does not exist

Missed a call in the previous fix.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Pull two documentation build fixes from Jonathan Corbet:

 - The XFS online fsck documentation uses incredibly deeply nested
   subsection and list nesting; that broke the PDF docs build. Tweak a
   parameter to tell LaTeX to allow the deeper nesting.

 - Fix a 6.8 PDF-build regression

* tag 'docs-6.8-fixes3' of git://git.lwn.net/linux:
  docs: translations: use attribute to store current language
  docs: Instruct LaTeX to cope with deeper nesting

Pull USB fixes from Greg KH:
 "Here are some small USB fixes for 6.8-rc6 to resolve some reported
  problems. These include:

   - regression fixes with typec tpcm code as reported by many

   - cdnsp and cdns3 driver fixes

   - usb role setting code bugfixes

   - build fix for uhci driver

   - ncm gadget driver bugfix

   - MAINTAINERS entry update

  All of these have been in linux-next all week with no reported issues
  and there is at least one fix in here that is in Thorsten's regression
  list that is being tracked"

* tag 'usb-6.8-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb:
  usb: typec: tpcm: Fix issues with power being removed during reset
  MAINTAINERS: Drop myself as maintainer of TYPEC port controller drivers
  usb: gadget: ncm: Avoid dropping datagrams of properly parsed NTBs
  Revert "usb: typec: tcpm: reset counter when enter into unattached state after try role"
  usb: gadget: omap_udc: fix USB gadget regression on Palm TE
  usb: dwc3: gadget: Don't disconnect if not started
  usb: cdns3: fix memory double free when handle zero packet
  usb: cdns3: fixed memory use after free at cdns3_gadget_ep_disable()
  usb: roles: don't get/set_role() when usb_role_switch is unregistered
  usb: roles: fix NULL pointer issue when put module's reference
  usb: cdnsp: fixed issue with incorrect detecting CDNSP family controllers
  usb: cdnsp: blocked some cdns3 specific code
  usb: uhci-grlib: Explicitly include linux/platform_device.h

Pull tty/serial driver fixes from Greg KH:
 "Here are three small serial/tty driver fixes for 6.8-rc6 that resolve
  the following reported errors:

   - riscv hvc console driver fix that was reported by many

   - amba-pl011 serial driver fix for RS485 mode

   - stm32 serial driver fix for RS485 mode

  All of these have been in linux-next all week with no reported
  problems"

* tag 'tty-6.8-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
  serial: amba-pl011: Fix DMA transmission in RS485 mode
  serial: stm32: do not always set SER_RS485_RX_DURING_TX if RS485 is enabled
  tty: hvc: Don't enable the RISC-V SBI console by default

Pull x86 fixes from Borislav Petkov:

 - Make sure clearing CPU buffers using VERW happens at the latest
   possible point in the return-to-userspace path, otherwise memory
   accesses after the VERW execution could cause data to land in CPU
   buffers again

* tag 'x86_urgent_for_v6.8_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  KVM/VMX: Move VERW closer to VMentry for MDS mitigation
  KVM/VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH
  x86/bugs: Use ALTERNATIVE() instead of mds_user_clear static key
  x86/entry_32: Add VERW just before userspace transition
  x86/entry_64: Add VERW just before userspace transition
  x86/bugs: Add asm helpers for executing VERW

Pull irq fixes from Borislav Petkov:

 - Make sure GICv4 always gets initialized to prevent a kexec-ed kernel
   from silently failing to set it up

 - Do not call bus_get_dev_root() for the mbigen irqchip as it always
   returns NULL - use NULL directly

 - Fix hardware interrupt number truncation when assigning MSI
   interrupts

 - Correct sending end-of-interrupt messages to disabled interrupts
   lines on RISC-V PLIC

* tag 'irq_urgent_for_v6.8_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  irqchip/gic-v3-its: Do not assume vPE tables are preallocated
  irqchip/mbigen: Don't use bus_get_dev_root() to find the parent
  PCI/MSI: Prevent MSI hardware interrupt number truncation
  irqchip/sifive-plic: Enable interrupt if needed before EOI

Pull erofs fix from Gao Xiang:

 - Fix page refcount leak when looking up specific inodes
   introduced by metabuf reworking

* tag 'erofs-for-6.8-rc6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
  erofs: fix refcount on the metabuf used for inode lookup

Pull RCU pathwalk fixes from Al Viro:
 "We still have some races in filesystem methods when exposed to RCU
  pathwalk. This series is a result of code audit (the second round of
  it) and it should deal with most of that stuff.

  Still pending: ntfs3 ->d_hash()/->d_compare() and ceph_d_revalidate().
  Up to maintainers (a note for NTFS folks - when documentation says
  that a method may not block, it *does* imply that blocking allocations
  are to be avoided. Really)"

[ More explanations for people who aren't familiar with the vagaries of
  RCU path walking: most of it is hidden from filesystems, but if a
  filesystem actively participates in the low-level path walking it
  needs to make sure the fields involved in that walk are RCU-safe.

  That "actively participate in low-level path walking" includes things
  like having its own ->d_hash()/->d_compare() routines, or by having
  its own directory permission function that doesn't just use the common
  helpers.  Having a ->d_revalidate() function will also have this issue.

  Note that instead of making everything RCU safe you can also choose to
  abort the RCU pathwalk if your operation cannot be done safely under
  RCU, but that obviously comes with a performance penalty. One common
  pattern is to allow the simple cases under RCU, and abort only if you
  need to do something more complicated.

  So not everything needs to be RCU-safe, and things like the inode etc
  that the VFS itself maintains obviously already are. But these fixes
  tend to be about properly RCU-delaying things like ->s_fs_info that
  are maintained by the filesystem and that got potentially released too
  early.   - Linus ]

* tag 'pull-fixes.pathwalk-rcu-2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  ext4_get_link(): fix breakage in RCU mode
  cifs_get_link(): bail out in unsafe case
  fuse: fix UAF in rcu pathwalks
  procfs: make freeing proc_fs_info rcu-delayed
  procfs: move dropping pde and pid from ->evict_inode() to ->free_inode()
  nfs: fix UAF on pathwalk running into umount
  nfs: make nfs_set_verifier() safe for use in RCU pathwalk
  afs: fix __afs_break_callback() / afs_drop_open_mmap() race
  hfsplus: switch to rcu-delayed unloading of nls and freeing ->s_fs_info
  exfat: move freeing sbi, upcase table and dropping nls into rcu-delayed helper
  affs: free affs_sb_info with kfree_rcu()
  rcu pathwalk: prevent bogus hard errors from may_lookup()
  fs/super.c: don't drop ->s_user_ns until we free struct super_block itself

Pull vfs fixes from Al Viro:
 "A couple of fixes - revert of regression from this cycle and a fix for
  erofs failure exit breakage (had been there since way back)"

* tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  erofs: fix handling kern_mount() failure
  Revert "get rid of DCACHE_GENOCIDE"

1) errors from ext4_getblk() should not be propagated to caller
unless we are really sure that we would've gotten the same error
in non-RCU pathwalk.
2) we leak buffer_heads if ext4_getblk() is successful, but bh is
not uptodate.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

->d_revalidate() bails out there, anyway.  It's not enough
to prevent getting into ->get_link() in RCU mode, but that
could happen only in a very contrieved setup.  Not worth
trying to do anything fancy here unless ->d_revalidate()
stops kicking out of RCU mode at least in some cases.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

->permission(), ->get_link() and ->inode_get_acl() might dereference
->s_fs_info (and, in case of ->permission(), ->s_fs_info->fc->user_ns
as well) when called from rcu pathwalk.

Freeing ->s_fs_info->fc is rcu-delayed; we need to make freeing ->s_fs_info
and dropping ->user_ns rcu-delayed too.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

makes proc_pid_ns() safe from rcu pathwalk (put_pid_ns()
is still synchronous, but that's not a problem - it does
rcu-delay everything that needs to be)
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

that keeps both around until struct inode is freed, making access
to them safe from rcu-pathwalk
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

NFS ->d_revalidate(), ->permission() and ->get_link() need to access
some parts of nfs_server when called in RCU mode:
	server->flags
	server->caps
	*(server->io_stats)
and, worst of all, call
	server->nfs_client->rpc_ops->have_delegation
(the last one - as NFS_PROTO(inode)->have_delegation()).  We really
don't want to RCU-delay the entire nfs_free_server() (it would have
to be done with schedule_work() from RCU callback, since it can't
be made to run from interrupt context), but actual freeing of
nfs_server and ->io_stats can be done via call_rcu() just fine.
nfs_client part is handled simply by making nfs_free_client() use
kfree_rcu().
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

nfs_set_verifier() relies upon dentry being pinned; if that's
the case, grabbing ->d_lock stabilizes ->d_parent and guarantees
that ->d_parent points to a positive dentry.  For something
we'd run into in RCU mode that is *not* true - dentry might've
been through dentry_kill() just as we grabbed ->d_lock, with
its parent going through the same just as we get to into
nfs_set_verifier_locked().  It might get to detaching inode
(and zeroing ->d_inode) before nfs_set_verifier_locked() gets
to fetching that; we get an oops as the result.

That can happen in nfs{,4} ->d_revalidate(); the call chain in
question is nfs_set_verifier_locked() <- nfs_set_verifier() <-
nfs_lookup_revalidate_delegated() <- nfs{,4}_do_lookup_revalidate().
We have checked that the parent had been positive, but that's
done before we get to nfs_set_verifier() and it's possible for
memory pressure to pick our dentry as eviction candidate by that
time.  If that happens, back-to-back attempts to kill dentry and
its parent are quite normal.  Sure, in case of eviction we'll
fail the ->d_seq check in the caller, but we need to survive
until we return there...
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

In __afs_break_callback() we might check ->cb_nr_mmap and if it's non-zero
do queue_work(&vnode->cb_work).  In afs_drop_open_mmap() we decrement
->cb_nr_mmap and do flush_work(&vnode->cb_work) if it reaches zero.

The trouble is, there's nothing to prevent __afs_break_callback() from
seeing ->cb_nr_mmap before the decrement and do queue_work() after both
the decrement and flush_work().  If that happens, we might be in trouble -
vnode might get freed before the queued work runs.

__afs_break_callback() is always done under ->cb_lock, so let's make
sure that ->cb_nr_mmap can change from non-zero to zero while holding
->cb_lock (the spinlock component of it - it's a seqlock and we don't
need to mess with the counter).
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

->d_hash() and ->d_compare() use those, so we need to delay freeing
them.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

That stuff can be accessed by ->d_hash()/->d_compare(); as it is, we have
a hard-to-hit UAF if rcu pathwalk manages to get into ->d_hash() on a filesystem
that is in process of getting shut down.

Besides, having nls and upcase table cleanup moved from ->put_super() towards
the place where sbi is freed makes for simpler failure exits.
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

one of the flags in it is used by ->d_hash()/->d_compare()
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

If lazy call of ->permission() returns a hard error, check that
try_to_unlazy() succeeds before returning it.  That both makes
life easier for ->permission() instances and closes the race
in ENOTDIR handling - it is possible that positive d_can_lookup()
seen in link_path_walk() applies to the state *after* unlink() +
mkdir(), while nd->inode matches the state prior to that.

Normally seeing e.g. EACCES from permission check in rcu pathwalk
means that with some timings non-rcu pathwalk would've run into
the same; however, running into a non-executable regular file
in the middle of a pathname would not get to permission check -
it would fail with ENOTDIR instead.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Avoids fun races in RCU pathwalk...  Same goes for freeing LSM shite
hanging off super_block's arse.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>